Replacement for leather and method for making same

ABSTRACT

A REPLACEMENT FOR LEATHER WHICH IS A HOMOGENEOUS SHEET FORMED BY THE COMBINATION OF FIBROUS MATERIAL, A WATER BASE POLYURETHANE LATEX BINDER AND A HYDROGEN BONDER. THE LEATHER REPLACEMENT IS PRODUCED BY TREATING A FIBROUS WEB WITH A WATER BASE POLYURETHANE LATEX AND WITH A SOLUTION CONTAINING A HYDROGEN BONDER.

United States Patent Qflice Patented May 21., 1974 US. Cl. 162-146 8Claims ABSTRACT OF THE DISCLOSURE A replacement for leather which is ahomogeneous sheet formed by the combination of fibrous material, a waterbase polyurethane latex binder and a hydrogen bonder. The leatherreplacement is produced by treating a fibrous web with a water basepolyurethane latex and with a solution containing a hydrogen bonder.

This application is a continuation-in-part of Application Ser. No.843,238, filed July 18, 1969, now abandoned.

This invention relates to a product which will function as a replacementfor leather. It also relates to a process for producing the product.

In general, the product of this invention may be described as ahomogeneous sheet material formed by the combination of fibrousmaterial, a water base polyurethane latex, and a hydrogen bonder.

As is known, many attempts have been made in the past to produce areplacement for leather. While in some instances these products havebeen called synthetic leathers, they are for the most part layeredproducts of woven or knitted fabrics having a synthetic plastic coatingthereon. Such products have the inherent disadvantage in that once theouter layer is damaged by heat, abrasion, chemicals, etc., the productbecomes esthetically unacceptable. Furthermore, many existingmultilayered composite materials suffer from not being sufficientlyporous to read- I ily allow air or water to pass through them.

It is an object of the present invention to provide a replacement forleather possessing many of the physical characteristics of good qualityleather.

It is also an object of the present invention to provide a method forproducing the leather replacement of the instant invention.

It is a further object of the invention to produce a leather substitutewhich may be finished so as to have the appearance of leather. y

The above and other objects and advantages of the present invention willbe apparent from the following detailed description of the invention.

As mentioned above, the product of the present invention is ahomogeneous material formed by the combination of a fibrous material, awater base polyurethane latex, and a hydrogen bonder. The fibers whichare used with the polyurethane latex are primarily cellulosic fibers,such as jute, hemp, mercerized Kraft and the ordinary paper makingfibers. While synthetic fibers, such as acrylic, polyester andpolyamide, are also contemplated, they do not appear to impart any addedstrength characteristics to the end product. It is postulated that thereason for this stems from the fact that the polyurethane latex does notform as many bonds with the synthetic fibers as it does with thecellulose fibers. 1

Length and diameter of the various fibers used do not appear to presentany degree of criticality. For example, while jute fibers have anaverage diameter of approximately .02 mm. and an average length of about4.8 mm.,

South Hadley 2 it would appear that fibers having an average diameter offrom .01 mm. to .06 mm. and an average length of from 2.0 mm. to 6.0 mm.are acceptable.

Referring to the polyurethane resins employed in the latex form in thepresent invention they may generally be described as organic block typeanionic polymers wherein the organic blocks are either interrupted byshort segments carrying'salt-type groups or terminated by segmentscarrying salt-type groups. Such polyurethane resins do not contain anyfree isocyanate groups capable of reacting with subsequently addedhydrogen containing compounds so as to extend and chain link or curethem. In general, these resins have a predominantly hydrophobiccharacter, but owing to the presence of the anionic salttype groups theyhave hydrophilic centers which enable aqueous colloidal solutions oraqueous dispersions to be prepared from them.

The polyurethane latices may be prepared by reacting together a (1)predominantly linear compound having active hydrogen atoms, at least onehydroxyl group and a molecular weight of from 300 to 20,000, (2) apolyisocyanate and if desired, chain lengthening agents having reactivehydrogen atoms, and (3) a compound having at leastone hydrogen atomreactive with isocyanate groups and at least one anionic salt-type groupor group capable of anionic salt formation. In such materials the ratioof isocyanate groups to hydrogen atoms reactive with isocyanate groupsin the compounds capable of salt formation, is such that the groupscapable of salt formation present do not undergo reaction with theisocyanate groups, and the resulting polyurethane is subsequentlyconverted in part to the salt form by reaction with an organic orinorganic base in the case where groups capable of salt formation arepresent. The proportion by weight of the salt-type groups contained inthe polyurethane is more than 0.1% and not more than 5%, preferablybetween 0.4 and 2.0%, and, when the salt-type groups are carboxylgroups, then not more than 3%.

Of the first type of compounds listed, the polyhydroxy compound, such aspolyesters, polyacetals, polyethers and polyester amides are preferred.

As for the polyisocyanates, such compounds include any-aromatic andaliphatic diisocyanates such as 1:5- naphthylene diisocyanate,4,4'-diphenyldimethylmethane diisocyanate, diandtetralkyldiphenylmethane-4,4'-diisocyanates, 4,4'-dibenzyl diisocyanate,1:3-phenylene-diisocyanate, the isomers of toluylene diisocyanate, ifdesired in admixture, butane-1:4-diisocyanate, hexane-1:6-diisocyanate,dicyclohexylmethane-4,4'-diisocyanate, cyclohexane-'1:4-diisocyanate,etc. In general, the aliphatic diisocyanates are preferred.

Compounds which contain at least one hydrogen atom reactive withisocyanate group and at least one salt-type group or group capable ofsalt formation which may be used, if desired in admixture, include thefollowing, e.g.:

To achieve a sufiicient amount of salt-type groups in the polyurethanesthat are produced, the proportion by weight of the salt-type groupincorporated should be more than 0.1% and not more than 5%, and in thecase of the carboxylate group not more than 3%.

212.5 g. of an adipic acid-1,6-hexane diol-neopentylglycolpolyester(OI-I number 66.0) were reacted at 120 C. with 51 g. of 1,6-hexanediisocyanate. The adduct was dissolved at 55 in 800 ml. of acetone. Anaqueous solution of 18.25 g. of lysine and 70 ml. of 10 percentpotassium hydroxide solution in 50 ml. of water were added to thesolution of the adduct. When the reaction was complete, 450 ml. of waterwere added and acetone was distilled off. A stable dispersion wasobtained with an pH-value of 8 and a solid content of 41 percent. Thedispersion after drying yielded clear, elastic, high tensile strengthfoils.

EXAMPLE II 205 g. of an 1,6-hexanediol-phthalic acid-polyester (OH-number 60.0) were reacted at 120 C. for two hours with 35.5 g. of1,6-hexane diisocyanate. The adductwas dissolved in 800 m1. of acetone.A mixture of 3.76 g. of ethylene diamine, 7.65 g. of 1,3-propane sultoneand 35 ml. of 10 percent aqueous potassium hydroxide solution in 50 ml.of water was added. After addition of 340 m1. of water the acetone wasdistilled off. A 42 percent dispersion was obtained.

The process for making the products of the present invention maygenerally be described as the double saturation of the fibers employedin a fibrous web. Specifically, the preferred embodiment of the methodinvolves the formation of a fibrous web that is first saturated with awater base polyurethane latex, followed by a second saturation of theweb with a hydrogen bonder solution.

The following examples are given in order to more fully illustrate themethod of the invention and exemplify the products produced thereby. Allpercentages are weight percent unless otherwise indicated.

EXAMPLE III This example is given to show a procedure for preparing theproducts of the present invention.

500 g. of a bone dry fiber and 23,000 cc. of tap water were placed in abeater so as to form a slurry having a consistency of approximately2.1%. Approximately 695 cc. of the slurry was removed from the beaterand poured into a deckle box so as to form a fiber sheet. After formingand pressing the fiber sheet, the wet composition of the sheet wascalculated as approximately 45.5% fiber and 54.5% water.

The wet fibrous sheet was then placed on the surface of an aqueoussaturant solution, i.e., a polyurethane latex having 20% solids, andallowed to completely soak through from the bottom of the fiber sheet.The saturated sheet was then pressed to remove excess water and dried ina dryer at 250 F. for 40 minutes with turning of the sheet everyminutes. At this point the pressed and dried sheet was calculated tohave a polyurethane latex binder content of approximately 31.7%.

Next, the dried and pressed sheet was saturated again with a secondsolution comprising hydrogen bonder, 1% Triton X-100 which is a nonionicalkyl aryl polyether alcohol surfactant having 9-10 polyoxyethylenechain links and which is produced by Rohm & Haas Company, and 89% water.This saturant solution was alowed to completely soak through the sheetfrom the bottom thereof.

After further pressing and drying, the bone dry weight analysis of thesheet was 55.6% fiber, 31.7% polyurethane latex binder and 12.7%hydrogen bonder.

EXAMPLE IV This example is presented to show the comparison of typical.calf skin leather and a hand sheet made by the procedure of Example IIIwherein hemp pulp was employed as the fiber and urea as the hydrogenbonder:

Fiber hand Leather sheet Tensile, lb./1' strip x 170 158.0 Stretch,percent 50 x 47 13. 7 Edge tear, 1b./1' strip 312 x 282 219. 0Stiffness, Taber units 22 x 34 0.

The first value in the sequence of numbers represents a longitudinaldirection value and the second represents a cross direction value. 1

As is readily noted from the above, the saturated fiber hand sheet comesquite close to leather in the physical properties listed. a

EXAMPLE V This example is presented to demonstrate the elfect the secondsaturation has on the physical properties of the end product. In thisexample, a hand sheet was made following the procedure of Example III,except that the second or post-saturation of the sheet with the hydrogenbonder was not employed. As in Example IV hemp pulp constituted thefibrous material. The physical properties of the end product are asfollows:

Tensile--lbs./ 1" strip 164.0 Stretch-percent 9.1 Edge tearlbs./ 1"strip 53.0 Stiffness-Taber units 280.0

As is clear from the above results, the omission of the post-saturationstep produces an end product with less than desirable physicalcharacteristics as compared to leather. In particular, it exhibits greatstiffness and poor edge tear.

EXAMPLE VI Sample Edge tear, number Saturant Post saturant lb./1 strip 1None None 61 2 --do 17.7% urea 34 3 32.0% polyurethane latex None 48 4--31.3% polyurethane latex 13. urea- 235 5. 34.0% polyurethane latex None66 6- 34.1% polyurethane latex 11.5% urea 207 The above listed resultsreadily point up the synergistic effect that the double saturation hason the fibrous sheets. This eifect is even more significant than onemight expect in that the results show that one saturation without theother in some cases actually produces a physically weaker product thanwhere no saturation is employed.

EXAMPLE VII In this experiment, a hand sheet was prepared according tothe procedure of Example III. However, another hemp pulp was selected asthe fibrous material and the amount of hydrogen bonder, i.e., urea, inthe final product was determined to be 16.2%. The edge tear of thissample was found to be 209 lbs./1" strip.

While the post-saturant hydrogen bonder has 'been exemplified in theabove examples as urea, other hydrogen bonders, such as the substitutedureas, such as phenyl urea, propyl urea, tetramethyl urea, the methylolureas, etc., are also contemplated.

The percent by weight composition of the leather replacement end productof this invention may be varied depending on the intended use. Forexample, the fiber content may vary from about 35% to 85%, which mayinclude up to 10% synthetic fiber mixed with cellulosic fiber, thepolyurethane binder from about to 45%, and the hydrogen bonder fromabout 2% to 25%. For most applications, however, it has been found thatthe preferred ranges are 45% to 65% fi'ber, 25% to 35% polyurethanelatex binder, and 10% to hydrogen bonder.

Additionally, additives for either joining fibers together, preventingexcess bonding so as to impart softness, or promoting hydrogen bondingso as to increase the physical properties such as edge tear may beincluded in the process. Such additives include for example, fibersofteners, lubricants, coagulants and moistening agents.

As the products of the present invention are meant to function as areplacement for leather, it follows that they have as many end uses asleather. For example, the softer materials may be used for handbags,belts and the like, while the stiffer materials may be used in luggage,book binding, inner soles for shoes, etc.

Having thus described the invention, what is claimed is:

1. A process for the manufacture of a leather like product whichcomprises forming a sheet from an aqueous slurry containing from 35% to85% 'by weight of said product of fibers, said fibers being selectedfrom the group consisting of cellulose fibers and a mixture of cellulosefibers and up to 10% synthetic fibers, saturating said sheet with awater base polyurethane having anionic salt-type groups and no freereactive isocyanate groups, said polyurethane being present in an amountof from about 10% to 45% by weight of said product and then saturatingsaid sheet with an aqueous solution of a urea, said urea comprising 2%to by weight of said product.

2. The process of claim 1 wherein said fibers are cellulose fibers.

3. The process of claim 1 wherein said fibers are a mixture of celluloseand synthetic fibers, said synthetic fibers being present in an amountup to 10% by weight of said product.

4. A process for the manufacture of a leather replacement product whichcomprises forming a sheet from an aqueous slurry containing 40% to 65%by weight based on said product of cellulose fibers, saturating saidsheet with a water base polyurethane latex having anionic salttypegroups and no free reactive isocyanate groups, said latex being presentin an amount of trom about 25 to 35% by weight of said product, and thensaturating said sheet with an aqueous solution of urea in an amount offrom 1 0% to 20% by weight of said product.

5. A homogeneous sheet material comprising a fiberous Web firstsaturated with a water base polyurethane latex having anionic salt-typegroups and no free reactive isocyanate groups, and then with an aqueoussolution of a urea, said fibers forming said web being selected from thegroup consisting of cellulose fibers and a mixture of cellulose fibersand up to 10% synthetic fibers, and being present in an amount of from35 to 85 by weight of said sheet, said latex being present in an amountof from 10% to by weight of said sheet and said urea being present in anamount of from 2% to 25% by weight of said sheet.

6. The homogeneous sheet material of claim 5 wherein said fiberscomprise 40% to by weight of said sheet, said polyurethane latexcomprises 25 to 35 by weight of said sheet, and said urea comprises 10%to 20% by weight of said sheet.

7. The homogeneous sheet material of claim 6 wherein said fibers arecellulose fibers.

8. The homogeneous sheet material of claim 6 wherein said fibers are amixture of cellulose and synthetic fibers, said synthetic fibers beingpresent in an amount up to 10% by weight of said sheet.

References Cited UNITED STATES PATENTS 3,491,067 1/ 1970 Sellet 162-464X 3,595,732 7/1971 Tingerthal 11762.2 X

ROBERT L. LINDSAY, 1a., Primary Examiner US. Cl. X.R.

8116.2; 117-622, 76 P, UA; 162158, 169

